extreme isn't actually extreme until about wave 120.
From there the level of difficulty increase is immense.
OH, btw, BFGs and Rocket BFGs (Laser, Cannon, Rocket for BFGs; Add 1 more rocket to BFG to make rocket BFGs) will easily get you to 300 or 350 on easy without any problems.
lol, i thought it sucked too, but then i realized, this game has more option than any other game i've played before. Therefore keeping me more interested.